1. Field of the Invention
The present invention relates in general to a position sensor for sensing a position of a movable member, and more particularly to a position sensor which is installed in a door lock to sense or detect the position of a pivotal component of the door lock.
2. Description of the Prior Art
Nowadays, a so-called passive seat belt system has been proposed and put into practical use in the field of passenger motor vehicles, which is designed to automatically move a seat belt to a passenger restraining position when the vehicle door is closed.
For sensing the door closing, various sensors have been hitherto proposed, two of which will be outlined in the following in order to clarify the task of the invention. They are disclosed in Japanese Utility Model Second Provisional Publication No. 61-22011 and Japanese Patent Second Provisional Publication No. 61-49471, respectively.
In the former case, as is shown in FIG. 3 of the accompanying drawings, a micro switch "MS" is mounted in a door lock at a position above a latch plate "L". An actuating pin "A" of the switch "MS" is in contact with a peripheral side surface of the latch plate "L" as shown. Upon closing of the vehicle door, a striker "ST" secured to the vehicle body pushes back the latch plate "L" to the full-latch position as shown by a phantom line. During this, the peripheral side surface of the latch plate "L" moves and thus pushes the actuating pin "A" thereby causing ON or OFF condition of the switch "MS". With this, the open and close conditions of the door are detected.
In the latter case, a rotary switch is mounted outside of the door lock having its rotating shaft coaxially connected with a pivot shaft of the latch plate. Upon pivoting of the latch plate due to closing of the door, the rotating shaft is forced to pivot thereby causing ON or OFF condition of the rotary switch.
However, due to the inherent constructions, the above-mentioned conventional sensors have the following drawbacks.
That is, in the former case, the micro switch "MS" is easily affected by cold weather and dust. When, for example in winter, some parts of the switch "MS" are iced even weakly, the actuating pin "A" fails to closely follow the movement of the peripheral side surface of the latch plate "L". This causes malfunction of the switch "MS".
In the latter case, the entire construction of the door lock is bulky because of presence of the rotary switch coaxially mounted thereon. This makes installation of the door lock in the door difficult or at least troublesome. Furthermore, because the rotary switch is arranged outside of the door lock proper, it fails to have a satisfied resistance against water and dust.